Well, how'd YOU defend the GATES?

[danielxcutter]

Hmmm, I'm not an expert of the D&D system, but I do have a good idea. Make a 3D maze, one made of hundreds of sections that have portals to navigate between them instead of just corridors. The layout changes every few hours, and every single sections is filled with dozens of savage monsters with high spell resistance, as well as sadistic traps such as Gaseous Form + Gust Of Wind to seperate party members, or blasting them with several Disjunctions to take out magic items such as Ring Of Energy Immunity. Also, since a party trying to get the gates would be almost certainly be Evil, including spells such as Holy Smite or Protection From Evil would have a great effect. The walls of course have been lined with lead and admantium to prevent from simply breaking through.

And lastly, add a subtle pattern, in the form of monsters getting more powerful the closer you get to somewhere. When the BBEG catches on to it, he'll naturaly follow it. In this last room, make a fake Gate. When touched, the final trap is set off: Dozens of powerful explosive spells that deal sonic damage, or if possible force damage, followed by several Sphere of Annihilation spells combined with Rods of Cancelation for 2d6*10*n damage.

The gate itself is located in the core of the maze, cut off and inaccessible without tearing down the entire thing.